Generally, the two common forms of fluorescent lamps are the so-called"preheat" type and the"rapid-start" type. The "preheat" type of fluorescent lamp has heater current flow therethrough during lamp ignition and thereafter a voltage-sensitive starter, external of the lamp, opens and discontinues the above-mentioned heater current flow. However the"rapid-start" type of fluorescent lamp normally has current flow through each electrode not only during ignition but also during the operational period of the lamp. Thus, it can readily be seen that this continuous flow of heater current during operation of the rapid-start lamp is a cause for power loss in the system and an obvious and undesired cause for reduced operational efficiency.
In an effort to improve the energy efficiency of rapid-start fluorescent lamps, numerous suggestions and structural configurations have been suggested. For example, U.S. Pat. Nos. 4,052,687; 4,097,779; 4,114,968; 4,156,831 and 4,171,519; all of which are assigned to the assignee of the present application, provide numerous configurations for enhancing the operation of rapid-start fluorescent lamps. Primarily, each of the above-listed patents relates to rapid-start fluorescent lamps or bimetal type circuit breakers for fluorescent lamps whereby heater current flow is discontinued during lamp operation.
Although each one of the above-listed structures and techniques enchances and provides numerous advantages over prior known configurations and processes, it has been found that problems remain. More specifically, it has been found that bimetal type circuit breakers ordinarily require an electrical shunting material short-circuiting the leads of the circuit breaker during the rapid-start fluorescent lamp manufacturing process. During lamp processing, the circuit breaker is subjected to temperatures sufficiently high (about 300.degree. C.) which maintains the circuit breaker open. Since the electrode of the fluorescent lamp includes a coating which require activation during lamp manufacture, it is necessary for the electrode to be electrically heated by electrode current therethrough during this time. Therefore, it has been found necessary to provide a means for essentially removing the circuit breaker effect from the structure (e.g., by short-circuiting) until after the emissive materials of the electrode have been activated.
In order to accomplish the above-mentioned emissive material activation, the above-described electrical shunt is short-circuited across the circuit breaker to permit current flow to the electrode. However, once the emissive materials on its electrode have been processed it is necessary to remove the electrical shunt and to reactivate the bimetal circuit breaker employed with the rapid-start fluorescent lamp.
Although such structures have been and still are employed with relatively good results, it has been found that a circuit breaker wherein an electrical shunt is required does present problems of extra materials, added labor, increased defects and reduced productivity all of which increases cost and reduces manufacturing efficiency. Moreover, lamp processing introduces numerous oxidation problems deleterious to good welding which is also a problem associated with the heat required for correct sealing of the envelope surrounding the bimetal switch configuration.